We examine the global H i properties of galaxies in quarter billion particle cosmological simulations using gadget-2, focusing on how galactic outflows impact H i content. We consider four outflow models, including a new one (ezw) motivated by recent interstellar medium simulations in which the wind speed and mass loading factor scale as expected for momentum-driven outflows for larger galaxies and energy-driven outflows for dwarfs (Sigma < 75 km s(-1)). To obtain predicted H i masses, we employ a simple but effective local correction for particle self-shielding and an observationally constrained transition from neutral to molecular hydrogen. Our ezw simulation produces an H i mass function whose faint-end slope of -1.3 agrees well with observations from the Arecibo Fast Legacy ALFA survey; other models agree less well. Satellite galaxies have a bimodal distribution in H i fraction versus halo mass, with smaller satellites and/or those in larger haloes more often being H i deficient. At a given stellar mass, H i content correlates with the star formation rate and inversely correlates with metallicity, as expected if driven by stochasticity in the accretion rate. To higher redshifts, massive H i galaxies disappear and the mass function steepens. The global cosmic H i density conspires to remain fairly constant from z similar to 5 -> 0, but the relative contribution from smaller galaxies increases with redshift.

We study the physical conditions of the circumgalactic medium (CGM) around z = 0.25 galaxies as traced by H I and metal line absorption, using cosmological hydrodynamic simulations that include galactic outflows. Using lines of sight targeted at impact parameters from 10 kpc to 1 Mpc around galaxies with halo masses from 10(11)-10(13) M-circle dot, we study the physical conditions and their variation with impact parameter b and line-of-sight velocity Delta v in the CGM as traced by H I, Mg II, Si IV, C IV, O VI and Ne VIII absorbers. All ions show a strong excess of absorption near galaxies compared to random lines of sight. The excess continues beyond 1 Mpc, reflecting the correlation of metal absorption with large-scale structure. Absorption is particularly enhanced within about Delta v < 300 km s(-1) and roughly 300 kpc of galaxies (with distances somewhat larger for the highest ion), approximately delineating the CGM; this range contains the majority of global metal absorption. Low ions like Mg II and Si IV predominantly arise in denser gas closer to galaxies and drop more rapidly with b, while high ions O VI and Ne VIII trace more diffusely distributed gas with a comparatively flat radial profile; C IV is intermediate. All ions predominantly trace T similar to 10(4-4.5) K photoionized gas at all b, but when hot CGM gas is present (mostly in larger haloes), we see strong collisionally ionized O VI and Ne VIII at b <= 100 kpc. Larger halo masses generally produce more absorption, though overall the trends are not as strong as that with impact parameter. These findings arise using our favoured outflow scalings as expected for momentum-driven winds; with no winds, the CGM gas remains mostly unenriched, while our outflow model with a constant velocity and mass loading factor produce hotter, more widely dispersed metals.

We present the first definitive measurement of the absolute magnitude of RR Lyrae c-type variable stars (RRc) determined purely from statistical parallax. We use a sample of 242 RRc variables selected from the All Sky Automated Survey for which high-quality light curves, photometry, and proper motions are available. We obtain high-resolution echelle spectra for these objects to determine radial velocities and abundances as part of the Carnegie RR Lyrae Survey. We find that M-V,M-RRc = 0.59 +/- 0.10 at a mean metallicity of [Fe/H] = -1.59. This is to be compared with previous estimates for RRab stars (M-V,M-RRab = 0.76 +/- 0.12) and the only direct measurement of an RRc absolutemagnitude (RZ Cephei, M-V,M-RRc = 0.27 +/- 0.17). We find the bulk velocity of the halo relative to the Sun to be (W-pi, W-theta, W-z) = (12.0,-209.9, 3.0) km s(-1) in the radial, rotational, and vertical directions with dispersions (sigma(W pi), sigma(W theta), sigma(Wz)) = (150.4, 106.1, 96.0) km s(-1). For the disk, we find (W-pi, W-theta, W-z) = (13.0,-42.0,-27.3) km s(-1) relative to the Sun with dispersions (sigma(W pi), sigma(W theta), sigma(Wz)) = (67.7, 59.2, 54.9) km s(-1). Finally, as a byproduct of our statistical framework, we are able to demonstrate that UCAC2 proper-motion errors are significantly overestimated as verified by UCAC4.

Using time-resolved, mid-infrared data from the Wide-field Infrared Survey Explorer (WISE) and geometric parallaxes from the Hubble Space Telescope for four Galactic RR Lyrae variables, we derive the following Population II period-luminosity (PL) relations for the WISE [W1], [W2], and [W3] bands at 3.4, 4.6, and 12 mu m, respectively:

X-ray measurements suggest that the abundance of calcium in the intracluster medium is higher than can be explained using favored models for core-collapse and Type Ia supernovae alone. We investigate whether the "calcium conundrum" in the intracluster medium can be alleviated by including a contribution from the recently discovered subclass of supernovae known as calcium-rich gap transients. Although the calcium-rich gap transients make up only a small fraction of all supernovae events, we find that their high calcium yields are sufficient to reproduce the X-ray measurements found for nearby rich clusters. We find the chi(2) goodness-of-fit metric improves from 84 to 2 by including this new class. Moreover, calcium-rich supernovae preferentially occur in the outskirts of galaxies making it easier for the nucleosynthesis products of these events to be incorporated in the intracluster medium via ram-pressure stripping. The discovery of calcium-rich gap transients in clusters and groups far from any individual galaxy suggests that supernovae associated with intracluster stars may play an important role in enriching the intracluster medium. Calcium-rich gap transients may also help explain anomalous calcium abundances in many other astrophysical systems including individual stars in the Milky Way, the halos of nearby galaxies, and the circumgalactic medium. Our work highlights the importance of considering the diversity of supernovae types and corresponding yields when modeling the abundance of the intracluster medium and other gas reservoirs.

We examine the statistics of the low-redshift Ly alpha forest from smoothed particle hydrodynamic simulations in light of recent improvements in the estimated evolution of the cosmic ultraviolet background (UVB) and recent observations from the Cosmic Origins Spectrograph (COS). We find that the value of the metagalactic photoionization rate (Gamma(HI)) required by our simulations to match the observed properties of the low-redshift Ly alpha forest is a factor of five larger than the value predicted by state-of-the art models for the evolution of this quantity. This mismatch in Gamma(HI) results in the mean flux decrement of the Ly alpha forest being overpredicted by at least a factor of two (a 10 sigma discrepancy with observations) and a column density distribution of Ly alpha forest absorbers systematically and significantly elevated compared to observations over nearly two decades in column density. We examine potential resolutions to this mismatch and find that either conventional sources of ionizing photons (galaxies and quasars) must contribute considerably more than current observational estimates or our theoretical understanding of the low-redshift universe is in need of substantial revision.

We examine how HI and metal absorption lines within low-redshift galaxy haloes trace the dynamical state of circumgalactic gas, using cosmological hydrodynamic simulations that include a well-vetted heuristic model for galactic outflows. We categorize inflowing, outflowing, and ambient gas based on its history and fate as tracked in our simulation. Following our earlier work, showing that the ionization level of absorbers was a primary factor in determining the physical conditions of absorbing gas, we show here that it is also a governing factor for its dynamical state. Low-ionization metal absorbers (e. g. MgII) tend to arise in gas that will fall on to galaxies within several Gyr, while high-ionization metal absorbers (e.g. OVI) generally trace material that was deposited by outflows many Gyr ago. Inflowing gas is dominated by enriched material that was previously ejected in an outflow; hence, accretion at low redshifts is typically substantially enriched. Recycling wind material is preferentially found closer to galaxies, and is more dominant in lower mass haloes since high-mass haloes have more hot gas that is able to support itself against infall. Low-mass haloes also tend to re-eject more of their accreted material, owing to our outflow prescription that employs higher mass loading factors for lower mass galaxies. Typical HI absorbers trace unenriched ambient material that is not participating in the baryon cycle, but stronger HI absorbers arise in cool, enriched inflowing gas. Instantaneous radial velocity measures of absorbers are generally poor at distinguishing between inflowing and outflowing gas, except in the case of very recent outflows. These results suggest that probing halo gas using a range of absorbers can provide detailed information about the amount and physical conditions of material that is participating in the baryon cycle.

We report new observations of circumgalactic gas from the COS-Dwarfs survey, a systematic investigation of the gaseous halos around 43 low-mass z <= 0.1 galaxies using background QSOs observed with the Cosmic Origins Spectrograph. From the projected one-dimensional and two-dimensional distribution of C iv absorption, we find that Civ is detected out to approximate to 100 kpc (corresponding roughly to approximate to 0.5 R-vir) of the host galaxies. The Civ absorption strength falls off radially as a power law, and beyond approximate to 0.5 R-vir, no Civ absorption is detected above our sensitivity limit of approximate to 50-100 m angstrom . We find a tentative correlation between detected C iv absorption strength and star formation, paralleling the strong correlation seen in highly ionized oxygen for L similar to L* galaxies by the COS-Halos survey. The data imply a large carbon reservoir in the circumgalactic medium (CGM) of these galaxies, corresponding to a minimum carbon mass of greater than or similar to 1.2 x 10(6) M circle dot out to similar to 110 kpc. This mass is comparable to the carbon mass in the interstellar medium and exceeds the carbon mass currently in the stars of these galaxies. The Civ absorption seen around these sub-L* galaxies can account for almost two-thirds of all W-r >= 100 m angstrom C iv absorption detected at low z. Comparing the Civ covering fraction with hydrodynamical simulations, we find that an energy-driven wind model is consistent with the observations whereas a wind model of constant velocity fails to reproduce the CGM or the galaxy properties.

We combine cosmological hydrodynamic simulations with analytic models to evaluate the role of galaxy-scale gravitational torques on the evolution of massive black holes at the centers of star-forming galaxies. We confirm and extend our earlier results to show that torque-limited growth yields black holes and host galaxies evolving on average along the M-BH-M-bulge relation from early times down to z = 0 and that convergence onto the scaling relation occurs independent of the initial conditions and with no need for mass averaging through mergers or additional self-regulation processes. Smooth accretion dominates the long-term evolution, with black hole mergers with mass ratios greater than or similar to 1: 5 representing typically a small fraction of the total growth. Winds from the accretion disk are required to eject significant mass to suppress black hole growth, but there is no need for coupling this wind to galactic-scale gas to regulate black holes in a nonlinear feedback loop. Torque-limited growth yields a close-to-linear <(M) over dot(BH)> proportional to star formation rate (SFR) relation for the black hole accretion rate averaged over galaxy evolution timescales. However, the SFR-AGN connection has significant scatter owing to strong variability of black hole accretion at all resolved timescales. Eddington ratios can be described by a broad lognormal distribution with median value evolving roughly as lambda(MS) (1 + z)(1.9), suggesting a main sequence for black hole growth similar to the cosmic evolution of specific SFRs. Our results offer an attractive scenario consistent with available observations in which cosmological gas infall and transport of angular momentum in the galaxy by gravitational instabilities regulate the long-term co-evolution of black holes and star-forming galaxies.